Development of a pulsed laser imaging system for natural gas leak detection

摘要

The detection of gas leaks represents a critical operation performed regularly by the gas industry to maintain the integrity and safety of its vast network of piping, both above and below the ground. We are developing a technology that allows the real-time imaging of gas plumes in a television format. Termed backscatter absorption gas imaging (BAGI), the technique operates by illuminating a scene with infrared laser radiation having a wavelength that is absorbed by the gas to be detected (in this case, methane). Backscattered laser radiation is used to create a video image of the scene. If a leak of the target gas is present in the field-of-view of the camera, it attenuates a portion of the backscatter and creates a dark cloud in the video picture. The specific purpose of this project is to investigate a new method of accomplishing BAGI using a pulsed laser source. The efficacy of using BAGI to detect natural gas leaks has already been demonstrated using a first-generation gas imaging technology that was developed at Lawrence Livermore National Laboratories. That technique accomplishes imaging by scanning a continuous-wave infrared laser (infrared helium-neon laser, emitting at 3.39 (mu)m) across a scene at real-time video rates as the scene is imaged by a scanned infrared camera. The primary limitation to the use of that system is the weak output energy of the helium neon laser (30 mW). The pulsed laser imager under development in this project is expected to have a range ((ge)40 m) and sensitivity (<10 ppm-m) that will surpass the respective attributes of the scanned imager. The pulsed system will operate by flooding (rather than scanning) the imaged scene with pulses of laser radiation. Imaging will be accomplished using a focal-plane array camera that operates in a snapshot format. The higher power of the pulsed laser source and the more effective collection optics of the focal-plane array-based receiver will allow the performance enhancements to be achieved.